The invention pertains to the field of lead-frames for attachment to an integrated circuit device (sometimes hereafter also referred to as "die" or "integrated circuit die"). More particularly, the invention pertains to leadframes for high power integrated circuit applications such as high power linear operational amplifier circuits wherein the design of the leadframe is enhanced to improve the thermal performance of the integrated circuit die.
Cooling of integrated circuit die is often an important requirement, especially in high power applications. Heating of an integrated circuit die through internal power dissipation in the circuit elements formed thereon causes several deleterious effects. First, heating of the die can adversely affect the electrical characteristics of semiconductor junctions formed in transistors and diodes. Excessive junction temperature can cause changes in key electrical parameters, and can cause thermal runaway if not properly compensated. Further, differences in the coefficients of thermal expansion between aluminum, silicon, polysilicon, and oxide passivation layers and the plastic encapsulant material of the package, can lead to cracking of passivation layers thereby creating paths through which water vapor and other impurities may penetrate from the outside of the die to the underlying circuit structures. Water vapor in contact with aluminum can cause corrosion.
The principal mechanism by which integrated circuit die are cooled is conduction to the outside world through the leadframe. A leadframe is a metallic structure which supports the integrated circuit die and provides conductive paths from the connection pads on the integrated circuit die to pins which are used to make connections to external elements such as integrated circuit sockets or printed circuit boards.
One such leadframe which has been in use for several years by National Semiconductor Corporation, the assignee of the present invention, is called the "Batwing" leadframe. This design is shown in the FIG. 2 and is prior art. The principal paths of heat conduction away from the integrated circuit die attach pad 1 are the four shortest rectangular paths 2, 3, 4 and 5 leading from the die attach pad to four external pins at 6, 7, 8 and 9 which are normally connected by conductive paths (not shown) to a ground plane (not shown) on a printed circuit board (also not shown).
The "batwing" leadframe design provides acceptable cooling efficiency. However, as line widths decrease and it is possible to pack more and more power generating elements on a single integrated circuit die, there continues to be a need for improved heat dissipation capabilities for leadframes.